1. Field of the Invention
This invention relates to an apparatus for mixing a fluid, such as a heavy oil, and particles, such as a catalyst, heated at elevated temperatures.
2. Prior Art
Reaction systems are known in which solid particles, as a catalyst or a heat medium, are brought into contact with a reactant. Moving bed type reactors are a typical example of such reaction system, which reactors are classified into those utilizing a concentrated fluidized bed (bubbles-fluidized bed) and those utilizing a high-speed moving bed (fluidized bed). The high-velocity moving bed is used for a reaction in which a solid and a gas must come into contact for a short period of time. Currently, an upflow-type high-velocity moving bed reactor, a so-called xe2x80x9criser-type,xe2x80x9d has mainly been employed in a fluid catalytic cracking apparatus used for the production of a gasoline from a feed stock, such as a heavy oil. This reactor is capable of reducing contact time with an improvement of catalytic ability, leading to an enhancement of selectivity of a final product and suppression of unfavorable excessive cracking reactions.
Recently, a strong demand has been made for an enhancement in selective productivity of a gasoline or a light olefin, and an investigation has been conducted for use of a downflow type high-velocity moving bed reactor, which is free from back-mixing, which adversely affects an improvement of the selectivity.
When producing gasoline from a feed stock, such as a heavy oil, using a fluid catalytic cracking apparatus equipped with the existing upflow-type reactor having a high-speed moving bed, the contact reaction therein takes several seconds. In contrast, when producing a light olefin, the reaction time is required to be reduced on the order of 0.1 to 1.5 seconds. A rapid mixture of a feed stock and a catalyst and vaporization thereof at the inlet port of a reactor is indispensable, in order to conduct the contact reaction in a short period of time. Furthermore, it has become necessary to increase the recycle ratio of catalyst to oil to compensate for a reduction in conversion resulting from a shortened reaction time.
In view of this background, there has been demanded an apparatus which is capable of rapid mixture and vaporization of the feed stock and the catalyst at the inlet of the existing upflow-type reactor to form a high-speed moving bed, and which enables a recycle ratio of catalyst to oil several times greater than that (catalyst/oil ratio of 5-8) of a catalytic cracking apparatus for producing a gasoline from a feed stock, such as a heavy oil.
With the foregoing difficulties of the prior art in view, the present invention seeks to provide an apparatus which is capable of mixing a fluid and solid particles uniformly and rapidly.
According to the invention, there is provided an apparatus for mixing a fluid of a feed stock, such as a heavy oil, and particles of a catalyst for gasifying the fluid in a reactor, which comprises providing in the upper portion of the reactor a circular port through which the particles are fed, a moving bed-forming section disposed on and in communication with the reactor for forming the particles into an annular high-velocity moving bed by feeding the particles downwardly into the reactor while dispersing the particles circularly, an external fluid feed section located so as to spray the feed stock over the entire upper outer periphery of the annular moving bed passing through the reactor, and an internal fluid-feed section located so as to spray the fluid over the entire upper inner periphery corresponding to the outer periphery of the annular moving bed.
According to another aspect of the invention, there is provided an apparatus for mixing a fluid of a feed stock, such as a heavy oil, and the particles of a catalyst for gasifying the fluid, which comprises a plurality of stand pipes extending vertically, a distributing device for distributing the particles uniformly into the stand pipes, a mixing section positioned below the distributing device, from the interior of which the stand pipes extend to the upper interior of the mixing section to feed the particles thereto, a plurality of plates arranged in the mixing section and below the stand pipes for dispersing the particles falling therefrom outwardly in a radial direction, and a fluid-feed chamber arranged in the mixing section in surrounding relation to the outer periphery of each of the stand pipes to spray the fluid downwardly in a vertical direction in close proximity to and in surrounding relation to the entire outer periphery of the cylinder of particles falling from each of the stand pipes, so as to collide with the particles after being dispersed by the plates.
According to another aspect of the invention, there is provided an apparatus for mixing the fluid of a feed stock, such as a heavy oil, and the particles of a catalyst for gasifying the fluid, which comprises a plurality of stand pipes extending vertically, a distributing device for distributing the particles uniformly into the stand pipes, a mixing section positioned below the distributing device, from the interior of which the stand pipes extend into the upper interior of the mixing section to feed the particles thereto, a plurality of plates arranged in the mixing section and below the stand pipes for dispersing the particles falling therefrom outwardly in a radial direction, and a fluid-feed chamber arranged in the mixing section in surrounding relation to the outer periphery of each of the stand pipes to spray the fluid over the entire outer periphery of the cylinder of particles falling from each of the stand pipes.
It is necessary for a short contact reaction to conduct a rapid uniform mixture of and vaporization of a feed stock and particles (catalyst) at the inlet of a reactor. Therefore, it is required to supply a feed stock in the form of fine droplets, for example by means of a spray, and to disperse the catalyst uniformly in the form of solid particles. The uniform mixture can be effected in a wide space, but fails to be fully accomplished in a limited space. An extensive research and development to seek an alternative for solving the problem resulted in the following conclusion.
In this alternative solution, after a feed stock in droplet form is made finer to some extent by means of a spray nozzle, the sprayed feed stock is brought into collision with solid particles, so as to be further refined by impact caused by the collision. Importantly, solid particles are increased in surface area as much as possible, so that the surface thereof can entirely collide with the sprayed feed stock. Hereinafter, it is described what shape the particles take in order to have a large surface area in a limited space size.
Referring to FIGS. 9, 11 and 13, there are shown tubular reactors in a state that particles 153 flow downwardly with the volume thereof being controlled. FIGS. 10, 12 and 14 repectively show a cross-sectional view of each tubular reactor 150, 151 and 152 shown in FIGS. 9, 11 and 13. As shown in these figures, the flowing particles in the cross-section of each of the tubular reactors take simple forms, among which those shown in FIG. 10(c), 12 and 14 are suitable for uniform mixture. The shape of the flowing particles in the cross-section of the tubular reactors shown in FIGS. 10 (a) and (b) are not adequate, because the particles flows locally in one side of the reactor 150. Suitable shapes of flowing particles for rapid mixture are those having a large outer surface. The annular shape formed by the flowing particles as shown in FIG. 14 has the largest outer surface and thus is found to be suitable for rapid mixture. In view of the foregoing, the particles flowing in an annular form are most suitable for rapid uniform mixture in a tubular reactor while controlling an amount of the particles to be mixed.